Artificial intervertebral disc device

ABSTRACT

Artificial disc devices are disclosed that restore correct anatomical intervertebral spacing for damaged discs while maintaining a substantially normal range of biomechanical movement for the vertebrae between which they are implanted. The disc devices include center bearing and outer or annular bearing portions with the center bearing portion including generally axially extending locating surfaces which cooperate with the facing vertebral surfaces to resist migration. The outer bearing portion is for load bearing or load sharing with the center bearing portion and includes surfaces that extend radially toward the periphery of the vertebrae so that subsidence about the center bearing portion is minimized. Alternate forms of the disc devices include one with an axially enlarged center ball bearing having an annular ring bearing extending thereabout and another having upper and lower plate members with a central bumper member and a surrounding resilient annular member therebetween.

BACKGROUND OF THE INVENTION

[0001] Artificial disc technology has been employed to correct damagedspinal discs for relieving back pain and restoring or maintainingintervertebral spacing while attempting to minimize their constrainingeffects on the normal biomechanical movement of the spine. Two types ofartificial discs have generally been employed: the artificial total discwhich is designed to substitute for the entire disc, i.e. the annulus,nucleus and possibly the end plates as well; and the artificial nucleuswhere only the nucleus is replaced with the annulus and end platesremaining intact. The disc of the present invention is not intended tobe limited to one or the other of the above types.

[0002] A number of prior artificial disc devices include upper and lowermembers that are rigidly fixed to the adjacent upper and lowervertebrae. These fixed members sandwich a bearing therebetween alongwhich they can slide to allow for relative movement between the adjacentvertebrae, see, e.g. U.S. Patent Application Publication 2002/0035400.However, devices such as these usually require special surface materialsand/or surface treatments that allow for bone ingrowth for fixing themembers to the vertebrae. Moreover, these devices have had problems withmigration where the intermediate bearing body shifts out from betweenthe vertebrae, and thus generally require more complex shapes to formstops for resisting such disc shifting.

[0003] In a relatively early approach, a stainless steel ball wasemployed in the damaged disc area. The ball approach, while effective toprovide a good range of motion, tended to create subsidence problems.Over time, the ball would crush into the end plates as loading wasfairly concentrated over a small surface on the ball in engagement withthe plates. In other words, since these ball implants were not of a sizethat enabled the load of the spine to be distributed evenly thereacross,the end plates tended to subside or fall around the ball.

[0004] There also has been focus on simply replacing the nucleus with agelled substance either injected directly in the disc or provided inpouches to attempt to reinflate the annulus and provide for loadbearing. However, these approaches are limited in their use to patientswho have a substantially undamaged disc annulus.

[0005] Accordingly, there is a need for an artificial disc that does notsignificantly inhibit spine movement while still providing the loadbearing and spacer functions akin to that of a normal, healthy spinaldisc.

SUMMARY OF THE INVENTION

[0006] In accordance with one form of the present invention, anartificial disc device is provided including a central, enlarged bearingportion and an outer, annular bearing portion generally extending aboutthe central bearing portion and allowing for movement therebetween. Theinner or central, enlarged bearing portion preferably has a bodyincluding upper and lower arcuate surfaces or surface portions that canshift relative to the outer bearing portion as well as with respect tothe confronting surfaces of the spine, such as the end plates of thevertebrae. In this regard, the arcuate surfaces are not rigidly fixed tothe vertebrae and are curved so as to allow the upper and lowervertebrae to shift with respect to each other such as when the spine isbent from side to side or front to back and twists or turns. At the sametime, the enlarged central bearing portion can engage in smallindentations in the respective vertebral surfaces that keeps the centralbearing in a relative locked position thereby preventing lateralshifting with respect to the vertebrae so that the implant does notmigrate despite the shifting vertebrae above and below these bearingsurfaces. Thus, the enlarged central bearing portion locates theartificial disc device relative to the vertebrae.

[0007] The main body of the central bearing or bearing portion orbearing assembly including the arcuate bearing surfaces thereof can be ahard metallic material or alloy for load bearing purposes.Alternatively, a hard plastic could be employed to provide the centralbearing portion with resiliency under compressive loading. For shockabsorption, the bearing body may be provided with a hollow core or onethat is liquid or gel filled or filled with other elastic material. Tovary the give or compressibility of the central bearing body, the sizeof the core could be enlarged or decreased accordingly, or the modulusof elasticity of the body material can be varied.

[0008] In one preferred form, the outer bearing portion has a body thatincludes radially inner surfaces adjacent the arcuate surfaces adaptedor configured for allowing relative movement therebetween. The outerbearing shares the compressive loading generated between the vertebraevia upper and lower bearing surfaces or surface portions thereof so thatthe load is better distributed across the present artificial disc deviceminimizing localized forces thereon. With the provision of the outerbearing, the present device is well suited to avoid subsidence problemsas could occur in prior devices having highly localized loading thereon.

[0009] The outer bearing or bearing assembly also may be constructed toprovide improved shock absorption capabilities such as with an innerportion of the body that is softer than the harder outer portion. Forexample, an elastomeric layer of material can be employed betweenattached upper and lower bearing plates of the outer bearing, or thecore layer of an annular portion and/or an inner ball bearing portion ofthe outer bearing can be of elastomeric or liquid gelled material.Manifestly, material combinations can also be employed to achievedesired shock absorption proportions. The outer bearing can furtherinclude a compression limiter so as to maintain proper tolerancesbetween the outer bearing inner surfaces and the inner bearing surfacesin confronting relation therewith as the outer bearing is loaded. Inthis manner, the inner bearing maintains its freedom of movement despitethe compressive loading that is being borne by the outer bearing, aswill be described more fully hereinafter.

[0010] In one form, the artificial disc includes a central ball as theenlarged, central bearing portion with an annular body of the outerbearing extending thereabout. The upper and lower load bearing surfacesor surface portions of the outer bearing body preferably do not projectaxially as far toward the upper and lower vertebrae as the ball surfaceportions such as by having a larger radius of curvature than the radiusof the ball. In other words, the load bearing surface portions have amore gradual curvature than the center bearing surface portions or forthat matter they can have a flat configuration. This allows the enlargedball to seat in the indents in the end plates for positioning theartificial disc securely between the vertebrae while the annular body isalso effective in taking up the compressive loading between the upperand lower vertebrae.

[0011] In another form, the central bearing portion includes a pair ofgenerally dome-shaped shell members that ride on a generally sphericalinner bearing portion integral with the outer bearing portion forsliding thereover. In this regard, the inner bearing portion isintegrally connected to the outer bearing portion via a circumferentialweb wall. The domes or shells are sized relative to the inner sphericalbearing portion so that there are gap spaces between the peripheraledges of the domes and the web wall. The web wall positions the outer,annular load bearing portion such that interference with shifting of thedomes on the central spherical bearing portion is minimized.Alternatively, snap-fitting the domes in place over the inner ballbearing portion could be employed; however, the above describedloose-fitting construction is preferred to minimize binding of the domeshells under compressive load forces. In this manner, the domes canreadily slide on the inner ball portion and, at the same time, thevertebral end plates or other vertebral surfaces in engagement with thearcuate surfaces of the domes can also shift with respect thereto toprovide a bipolar device with two interfaces that shift with respect toeach other.

[0012] By having this bi-polar artificial disc construction, the stressand wear that would otherwise occur in either of the interfaces isdecreased as one bearing interface can be shifting when the load on theother becomes too great. Lubricant can be provided between the domeshells and the inner bearing portion to reduce friction and weartherebetween. A seal ring attached adjacent or at the end edge of theshells for being carried therewith minimizes lubrication leakage whileallowing the shells to slide over the spherical surface of the innerbearing portion in a low friction manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIGS. 1A-1E are directed to various views of one form of anartificial disc implant device in accordance with the present inventionshowing an enlarged spherical central bearing and an outer annularbearing;

[0014] FIGS. 1F-1J are directed to various views of a disc deviceslightly modified over that shown in FIGS. 1A-1E to better conform tothe vertebrae;

[0015] FIGS. 2A-2D are directed to various views of the artificial discdevice of FIGS. 1A-1E as implanted between adjacent upper and lowervertebrae;

[0016] FIGS. 3A-3D are directed to various views of an alternativeartificial disc in accordance with the present invention showing a pairof dome shells that ride on an inner, spherical bearing portion integralwith the outer annular bearing portion;

[0017] FIGS. 4A-4D are directed to various views of the artificial discdevice of FIGS. 3A-3D implanted between upper and lower vertebrae;

[0018] FIGS. 5A-5E are directed to various views of an artificial discdevice similar to that shown in FIGS. 3A-3D except having acircumferential groove extending about the periphery of the outerbearing portion;

[0019] FIGS. 6A-6F are directed to various views of another artificialdisc device in accordance with the present invention showing a pair ofouter, annular bearings that fit about an enlarged, central sphericalbearing;

[0020] FIGS. 7A-7C are directed to various views of an alternativeconstruction of the central bearing showing opposing dome shells, onehaving a central post projection and the other having a central hub;

[0021] FIGS. 8A-8E are directed to various views of an artificial discdevice including the dome shells of FIGS. 7A-7C projecting into anopening formed in the inner bearing portion;

[0022]FIG. 9 is a cross-sectional view of an alternate form of theartificial disc device of FIGS. 8A-8E showing a pair of inner bearingrings on which the respective dome shells ride with a cushion web walltherebetween.

[0023] FIGS. 10A-10D are directed to various views of anotheralternative artificial disc device having an axially enlarged centralbearing member and an outer, annular bearing member showing anhour-glass configuration for the central-bearing member and an aperturedbody of the outer bearing member;

[0024] FIGS. 10E-10H are directed to a modified version of the discdevice of FIGS. 10A-10D showing different sizes of through aperturesformed in the outer bearing member;

[0025] FIGS. 11A-11H are directed to various views of alternativeartificial disc devices showing upper and lower bearing members and aload bearing member therebetween; and

[0026] FIGS. 12A-12I are directed to various views of an alternativedisc device showing upper and lower plate members, and an annular loadbearing member and a plug member therebetween.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Referencing FIGS. 1A-1E, an artificial disc device 10 is shownwhich includes an enlarged, central bearing portion 12, and asubstantially annular, outer bearing portion 14 having a through opening15 in which the central bearing portion 12 is disposed. Herein,preferred shapes, configurations and material selections for the innerand outer bearing portions are set forth. However, in each case, theseselections are not meant to be limiting as other selections that servethe purpose of the disc implant described herein are also contemplated.Likewise, several embodiments are disclosed that have structuralfeatures that can be implemented substantially interchangeably among thedisc implants.

[0028] In the form illustrated in FIGS. 1A-1E, the central bearing 12has an axially enlarged body 13 relative to the outer bearing 14 so thatit generally includes arcuate surface portions 16 and 18 that projectabove and below the radially outer bearing portion 14 for engaging inindents in confronting surfaces 20 a and 22 a of the adjacent upper andlower vertebrae 20 and 22, respectively, for seating the implant 10therein. In the implant device 10, the central bearing 12 can be in theform of a generally spherical ball such that the surface portions 16 and18 are part of the outer spherical surface 24 thereof. The annularbearing portion 14 has a generally ring-shaped (e.g. circular, oval orellipsoidal) body 17 that includes an arcuate inner side surface 26extending about the opening 15 that faces the ball bearing 12 havinggenerally the same radius of curvature as that of the spherical ballsurface 24 so that the ball bearing 12 can substantially freely rotatein the small, concave indents, divots or depressions 27 and 29 formed inthe vertebrae confronting surfaces in which the ball 12 seats, asdescribed above and shown in FIGS. 2A-2D. At the same time, thevertebral surfaces 20 a and 22 a, and particularly the concave indents27 and 29 formed therein can readily slide over the ball surface 24. Theconfiguration and rotation of the ball bearing 12 allows the spinevertebrae 20 and 22 to substantially undergo the normal range ofbiomechanical movement such as when the patient is twisting their backand/or bending it in various directions.

[0029] When the implanted disc 10 undergoes compressive loading, theouter bearing 14, and in particular the upper and lower surface portions28 and 30 thereof will substantially maintain the effective spacingbetween the vertebrae 20 and 22. Thus, in the present artificial discdevice 10, the outer ring bearing body 17 shares the loading with theball bearing body 13 created between the dynamically moving vertebrae 20and 22 so as to avoid subsidence problems as occurred with prior ballbearing-type devices. Accordingly, in the disc 10, the outer bearing 14generally will not allow the end plates to subside around the ballbearing 12.

[0030] As shown, the curvature of the upper and lower surface portions28 and 30 of the outer bearing body 17 is more gradual than that of thearc surface portions 16 and 18 of the central ball bearing body 13 toprovide it with a doughnut-type configuration. Accordingly, in thedevice 10, the surface portions 28 and 30 are part of a substantiallycontinuously curved outer ring bearing surface 32 such that they curvearound the radially outermost point 29 of the outer bearing body 17 toform an outwardly projecting convex configuration 29 for the outersurface 32 of the annular bearing 14. As such, the surface portions 16and 18 extend to their greatest spacing at the central section 17 aadjacent the central opening 15 of the bearing body 17. At the thickestsection 17 a, the spacing of the surface portions 16 and 18 is less thanthe diameter of the ball bearing 12 so that the surface portions 16 and18 protrude from the opening 15 to extend above and below the respectiveouter bearing surface portions 28 and 30 for engaging in the concavedepressions 27 and 29. The gradual curvature of the surface portions 28and 30 allows the ring bearing 14 to better conform to the generalconcavity of the vertebral surfaces 20 a and 22 a including any attachedend plates over time. By way of example and not limitation, the ballbearing diameter can be approximately between 6-18 mm and the maximumthickness of the outer bearing section 17 a can be approximately 16 mm.Manifestly, these sizes are to be tailored according to the anatomy ofthe patient being treated.

[0031] Referring to FIGS. 1F-1J, artificial disc device 10 a is depictedwhich has a slightly modified wedged or bulged configuration forcorresponding outer bearing body 14′ thereof. More particularly, as canbe seen in the cross-sectional view of FIG. 1J, the outer bearing body14′ has a thickened section 17 a and thinner section 17 b as measuredbetween the corresponding upper and lower surface portions 28 a and 30 awith these sections being generally diametrically opposite each otherwith a smooth transition therebetween. Since the confronting verticalsurfaces 20 a and 22 a will normally be in a non-parallel orientationrelative to each other, the section 17 a of the disc device 10 a willbetter conform to the area between the surfaces 20 a and 22 a that arespaced further from each other with the section 17 b fitting better inthe more confined, closely spaced area between the vertebrae surfaces 20a and 22 a allowing the implant device 10 a to be tightly fit or wedgedbetween the vertebrae 20 and 22.

[0032] With the vertebrae 20 and 22 exerting compressive loading on theartificial disc device 10, the projecting surface portions 16 and 18 ofthe center ball bearing 12 will securely engage in the indented recesses27 and 29 in the confronting vertebral surfaces 20 a and 22 a forseating the ball bearing 12 therein. As the spine moves causing relativeshifting of the vertebrae 20 and 22 about the ball bearing 12 with itfreely rotating in the recesses 27 and 29 as necessary, further loadingis exerted on the device 10, with the surface portions 28 and 30 of theouter annular bearing 14 being effective to share with the ball bearing12 the compressive loading that is generated between the vertebrae 20and 22, and which further can act as a shock absorber for the highimpact load bearing that may be needed between the vertebrae 20 and 22,such as described hereinafter. In this manner, the present artificialdisc device 10 resists both migration by the seating of the central ballbearing 12 as well as avoiding subsidence problems by providing loadbearing which is well distributed across a large radially extendingsurface area of the device 10 as by the device upper surfaces 16 and 28and lower surfaces 18 and 30. For example, the distance from the centralaxis 19 of the ring bearing 14 extending through the opening 15 to theouter end 29 can be approximately 12 mm.

[0033] While other material selections are possible, it is presentlycontemplated that the inner ball bearing 12 preferably will be of aharder material than the outer bearing 14 so that the harder ball 12 ismore apt to maintain its conformity with and thus stay seated in theindents 27 and 29 in the surfaces 20 a and 22 a. In this regard, theball 12 can be of a biocompatible material including titanium ormetallic material such as stainless steel, while the ring bearing 14 canbe of a material of a lower modulus of elasticity such as plasticmaterial, e.g polyethylene, so as to have some resilience undercompressive loading forces.

[0034] With a plastic outer bearing 14, a support hoop 34 of a hardermaterial than that of the outer bearing 14 such as of metal materialsimilar to that of the ball bearing 12 can be embedded therein.Generally, the hardness of the ball bearing 12 and the hoop 34 will bothbe greater than the outer bearing 14, although they may not be the sameas each other. For example, the hoop 34 can be of a hard metal materialwhereas the center bearing 12 can have a hardness similar to the humanbone. To this end, the plastic outer bearing 14 can be a moldedcomponent of the artificial disc device 10. As such, the metal supporthoop 34 can be molded in situ in the outer ring bearing 14. The supporthoop 34 serves as a compression limiter to resist deformation of theresilient plastic ring bearing 14 due to the compressive loadinggenerated between the vertebrae 20 and 22 so that it is better able tomaintain its configuration despite the stresses exerted thereon. Inaddition, the hoop 34 also resists shear forces generated by spinalmovements for reducing such forces in the resilient material of theouter bearing 14.

[0035] Alternatively, outer bearing body 17 can have an inner coreportion that is of different and softer material than that of the harderouter portion so that the annular bearing 14 has improved shockabsorbing properties for high force impacts on the artificial disc 10with the harder outer layer minimizing wear on the bearing 14. Forexample, the wear layer can be of hard polyethylene material with theinner cushion material of the bearing body 17 being of a softerpolymeric or elastomeric material. In another alternative, the body 17can include a hollowed inner portion that is filled with liquid or gelor other elastic material, e.g. Hydrogel and/or polyurethane, for shockabsorption purposes.

[0036] FIGS. 3A-3D and 5A-5E are directed to alternative artificial discdevices 36 and 38, respectively. The disc devices 36 and 38 are ofsimilar construction as each include a central bearing portion 39 formedfrom two opposing shells 40 and 42 having a generally dome-shapedconfiguration riding on a central or inner, spherical ball bearingportion 44 that can be formed integrally with a body 43 of radiallyenlarged bearing 46 including outer bearing portion 45 thereof. Oppositeupper and lower annular arcuate spaces 43 a and 43 b are formed in thebody 43 separating the bearing portions 44 and 45 by a distance greaterthan the thickness of the shells 40 and 42 so that respective shell endportions 47 and 49 fit therein allowing the dome shells 40 and 42 toslide on the ball bearing portion 44.

[0037] Other differences in the construction of the bearing 46 of thedevices 36 and 38 relates to the plan configuration of the outer bearingportion 45. The devices 36 and 38 have their bearing portion 45 providedwith a pair of lobe sections 48 and 50 that extend in a continuouslycurved path about the majority of their peripheries until the lobeperimeters meet at their juncture formed at a recessed area 52therebetween. In this manner, the plan shape of the lobed bearing 46more closely approximates that of the vertebrae 20 and 22 between whichthe devices 36 and 38 are implanted. Ring bearing 14 could be providedwith a similar lobed plan configuration. Manifestly, the outer bearings14 and 46 can be formed with other configuration, e.g. oval in plan, soas to be more closely match that of the intervertebral space in whichthey are to be implanted.

[0038] Another difference resides in the configurations of load bearingsurface portions 54 and 56 of the bearing 46 generally corresponding tothe load bearing surface portions 28 and 30 of the bearing 14. Incontrast to the curvature of the surfaces 28 and 30 of the ring bearing14, the surfaces 54 and 56 are shown as having a generally flat,parallel configuration so that the bearing body 43 has more of a disc orplate-like configuration. Generally, however, some curvature on thesebearings surfaces 54 and 56 will be desirable although perhaps modifiedfrom that shown for bearing surfaces 28 and 30 for the implant 10. Thesurfaces 54 and 56 are provided with a spacing smaller than that of thediameter of the central bearing portion 44 and thus of the centralbearing assembly 39 with the dome shells 40 and 42 thereon so that theyproject above and below the respective surfaces 54 and 56. In thismanner, the dome shells 40 and 42 are able to seat in indents 27 and 29in the vertebral surfaces 20 a and 22 a like the bearing ball surfaceportion 16 and 18. To this end, the shells 40 and 42 can be of hardermaterial than that of the bearing body 43, and particularly the ballbearing portion 44 thereof. Accordingly, similar to the ball bearing 12,the dome shells 40 and 42 can be of a ceramic material or astainless-steel metal, titanium or alloys thereof, whereas the ringbearing 46 is preferably of a plastic or polymer material such aspolyethylene to provide it with stiffness and resiliency undercompressive loading. The bearing 46 could also be of like material tothat of the dome shells 40 and 42 for higher load bearing capacity.

[0039] The dome shells 40 and 42 are sized relative to the sphericalbearing portion 44 such that there are gap spacings 57 betweenperipheral end edges 58 and 60 of the respective shells 40 and 42 attheir largest diameters and web wall 62 in the bearing 46, as best seenin the cross sectional views of FIGS. 3D and 5D. Accordingly, thediameter across the end edges 58 and 60 of the dome shells is less thanthe diameter of the ball bearing portion 44. In use, the dome shells 40and 42 can slide to take up these spaces 57.

[0040] The web wall 62 extends laterally or radially and centrally fromthe ball bearing portion 44 to the annular load bearing portion 45 thatextends about the ball bearing portion 44 on which the shells 40 and 42ride. The circumferential web wall 62 extends radially for a sufficientdistance, such that the outer bearing portion 45 is spaced from the ballbearing portion 44 to provide recesses 43 a and 43 b large enough toallow the dome edges 58 and 60 to slide into engagement with the webwall 62 without encountering interference from the annular load bearingportion 45 of the bearing 46.

[0041] In the device 38, the annular bearing portion 45 includes aradially inner surface 51 that extends generally axially or tangentiallyto outer spherical surface 44 a of the inner bearing portion 44, albeitspaced slightly therefrom via web wall 62. In this manner, thecorresponding spaces 43 a and 43 b in the body 43 of the device 38 areenlarged over those in device 36 such that overhanging portions of thebearing portion 45 that can be compressed against the dome shellportions 47 and 49 and potentially cause binding in the spaces 43 a and43 b are avoided.

[0042] With the above-described construction, the artificial discdevices 36 and 38 have a bi-polar construction in that relative movementbetween the vertebrae 20 and 22 and the dome shells 40 and 42 can occuralong with relative movement between the dome shells 40 and 42 and theball bearing portion 44. Generally, the smooth surface interface betweeninner surfaces 40 a and 42 a of the respective shells 40 and 42 and theouter surface 44 a of the ball bearing portion 44 will have a lowercoefficient of friction therebetween than that between outer surfaces 40b and 42 b of the respective shells 40 and 42 and the indents 27 and 29in the vertebrae surfaces 20 a and 22 a. Thus, there will be somedifferential shifting that can occur with the moving components of thedevices 36 and 38 such that generally the domes 40 and 42 will morereadily shift along the ball bearing portion 44 prior to shifting of thedome shells 40 and 42 with respect to the vertebrae 20 and 22. Suchdifferential articulation keeps wear between the higher coefficient offriction surfaces to a minimum as sliding can preferentially occurbetween the smooth inner arcuate surfaces 40 a and 42 a of therespective shells 40 and 42 and the outer surface 44 a of the ballbearing portion 44. Alternatively, if the coefficient of friction islower between the vertebrae surface concave indents 27 and 29 and theshell outer surfaces 40 b and 42 b, then of course shifting willpreferentially occur at this interface of the disc devices 36 and 38keeping wear at the higher friction interface between the shell innersurfaces 40 a and 42 a and ball surface 44 a to a minimum. Of course, asthe spine is undergoing various dynamic forces during the movements itis required to undertake, oftentimes both interfaces of the bi-polardevices 36 and 38 will be shifting simultaneously to provide the spinewith the necessary biomechanics while also keeping undue wear on thedisc devices 36 and 38 to a minimum.

[0043] FIGS. 4A-4D illustrate the lobed artificial disc device 36implanted between the adjacent upper and lower vertebrae 20 and 22. Inthe view of FIG. 4C, the disc device 36 is employed with the annulus 65kept intact, and in the other view, the annulus 65 is removed with thedisc device 36 implanted. To maintain the annulus 65, the disc device 36is inserted through an incision in the annulus 65 which may be repairedonce the device 36 is implanted. In this instance, the device 36reinflates the annulus 65 keeping it taut and relieves the compressiveloading on the annulus 65. The other artificial disc devices describedherein can be employed in a like manner to that of device 36.

[0044] The annular load bearing body portion 45 of the device 36 has anouter peripheral surface 66 (FIG. 3C) with a generally convexconfiguration similar to the convex curved configuration at thecorresponding radially outer location of the outer annular bearing 14.In contrast, the corresponding surface 68 of the load bearing portion 46of the device 38 shown in FIG. 5C has a grooved or concave configurationto form thinned upper and lower flange rims 70 and 72 thereof. Theabove-described construction for the bearing 46 as shown in FIG. 5Cprovides it with greater flexibility as the flanges 70 and 72 are betterable to flex toward each other under compressive loading and thus areoptimized from a shock absorption standpoint. In particular, by havingthe flanges 70 and 72 extending around the entire circumference of thebearing 46, compressive loads taken locally by the bearing 46 such asdue to bending of the spine in a particular direction will cause theportions of the flanges 70 and 72 thereat to flex toward each otherabout the concave peripheral surface 68 while the remainder of the disc46 including the unloaded portions of the flanges 70 and 72 will remainsubstantially undeformed. Once this loading is removed, the bent portionof the flanges 70 and 72 can resiliently flex back to their illustratedsubstantially undeformed configuration. In this manner, the flanges 70and 72 better permit directional deformation of the bearing 46.

[0045] Optionally, upper and lower annular layers including the flanges70 and 72 can be provided of harder material than a more flexible corematerial of the bearing body 43 for optimized wear resistance at theinterfaces with the vertebral surfaces 20 a and 22 a and also forimproved shock absorbing properties for the device 38 a. For instance,the wear layers can be of hard polyethylene while the core of the body43 would be of more flexible, e.g. elastomeric, cushioning material.

[0046] Referring next to FIGS. 6A-6F, another artificial disc device 74in accordance with the invention is illustrated. The artificial discdevice 74 is similar to the device 10 of FIGS. 1A-1E in that it includesa central ball bearing 76 such as of ceramic material or stainless steelor titanium metal and alloys thereof or having carbon fiber or otherbiocompatible materials therein and including projecting arc surfaceportions 78 and 80 for seating in the indents 27 and 29 in the vertebralsurfaces 20 a and 22 a, as previously described. The device 74 ismodified over device 10 in that rather than having a doughnut shapedbearing 14, the device 74 includes a pair of annular plates or discs 82and 84 such as of a metallic material vertically spaced along centralaxis 86 that extends through the central openings 88 and 90 formed inthe respective discs 82 and 84 in which the ball bearing 76 is received.As shown, the disc openings 88 and 90 are of a maximum diameter that isslightly less than that of the diameter of the ball bearing 76 such thatwhen the arcuate surfaces 83 and 85 about the openings 88 and 90 are inclose fit with the outer ball surface 92 and the discs 82 and 84 are ina generally parallel orientation, the discs 82 and 84 will be spaced bya gap 94 therebetween.

[0047] With the device 74 loaded and the confronting vertebral surfaces20 a and 22 a engaging and pushing on the discs 82 and 84, they willshift and pivot relative to each other and axis 86 closing the gap 94 atcertain locations thereabout and opening it at others. As such, it isthe upper surface 82 a and lower surface 84 a of the respective upperand lower discs 82 and 84 that are the major load bearing surfaces forthe device 74. As shown, these surfaces 82 a and 84 a can be contouredso that the respective discs become thicker as extending from theperiphery toward the respective openings 88 and 90 of the discs 82 and84.

[0048] In an alternative form, a resilient and flexible cushioningmaterial 95 can be attached between the discs 82 and 84. The material 95will keep the unloaded discs 82 and 84 in the illustrated, generallyparallel orientation, but also allow them to undergo relative shiftingunder compressive loading. In this regard, the material 95 is selectedso that it can resiliently expand and contract as the discs 82 and 84shift and tilt or pivot with respect to each other. Alternatively, theunloaded discs 82 and 84 could be canted to a nonparallel orientationrelative to each other to provide the disc device 74 with a wedgedconfiguration similar to the previously-described device 10 a.

[0049] Accordingly and as described above, as the spine and particularlythe vertebrae 20 and 22 exert compressive loading on the discs 82 and84, they can shift relative to one another so they are better able toconform to the position of the vertebrae 20 and 22 as they shift withspine movement. For example, if the patient bends anteriorly, the upperdisc 82 can tilt relative to the axis 86 so the gap spacing 94 betweenthe discs 82 and 84 can be greater at the rear portion than at theforward portions thereof. In a like manner, if the patient bends theirspine posteriorly, then the upper disc 82 can pivot about axis 86 suchthat the gap spacing 94 can be greater at the forward portions relativeto the spacing at the rear portions. In each instance described above,there will usually be some tilting of the lower disc 84 as well althoughnot to the same degree as that of the upper disc 82 so that theirtilting movements relative to the axis 86 generally will correspond tothat of the upper and lower vertebrae 20 and 22 and the surfaces 20 aand 22 a thereof relative to the axis of the spine.

[0050] The discs 82 and 84 can have a plan configuration akin to that ofthe lobed bearing 46, or alternatively they can be oval or ellipsoidal.As shown in the plan view of FIG. 6D, the configuration of the discs 82and 84 includes a larger recessed or concave area 94 as compared withthe corresponding recess area 52 of the ring bearing 46. Further, thecurvature of the remainder of the disc periphery 96 varies from aconvexly curved portion 98 opposite the recessed area 94 to straighteropposite sides 100 and 102 on either side of the recessed area 94.

[0051] Turning to FIGS. 7A-7C, an alternative construction for thecentral bearing 39 is shown. In this version, a pair of opposing domes104 and 106 are provided which ride on an inner bearing portion 107similar to previously-described ball bearing portion 44, albeit modifiedto accommodate the projecting post 108 and hub 110, which are describedbelow.

[0052] The hub 110 can have a recess 112 which can engage against thedistal curved end 114 of the post 108 to resist the compressive forcesthat otherwise would push the dome shells 104 and 106 further towardeach other. More particularly, the dome shell 104 has an end edge 116and the post 108 extends centrally from the shell 104 along axis 118 sothat it projects beyond the edge 116. Likewise, the shell 106 includesan end edge 120 beyond which the hub 110 can project along the centralaxis 118 so that it is in alignment with the post 108. The post 108 andhub 110 have their respective sizes coordinated so that they define alimit at which spacing 122 between the dome shells 104 and 106 cannot beexceeded with the end edges 116 and 120 extending generally parallel toeach other. In this manner, unlike the previously described centralbearing assemblies 39 that rely on the stiffness or resilience of thepolymeric spherical bearing portion 44 to resist compression of the domeshells 40 and 42, the dome shells 104 and 106 which are preferably of aharder material such as metal employ the cooperating integral post 108and hub 110 for limiting the maximum compression that can occurtherebetween. As is apparent, under normal conditions, the post 108 andhub 110 will be spaced or only lightly engaged so that they do not bearthe loads generated between the vertebrae 20 and 22.

[0053] As mentioned above and referencing FIGS. 8A-8E, the central orinner bearing portion 107 is modified so that the post 108 and hub 110can project therethrough. As seen in the cross-sectional view of FIG.8E, the bearing portion 107 has an axial through opening 124 havingreversely configured upper and lower frustoconical surface portions 124a and 124 b into which the post 108 and hub 110 extend, respectively.The surface portions 124 a and 124 b taper from the largest size of theopening 124 at the dome surfaces to the smallest size of the opening 124at the center of the ball bearing portion 107. This provides the domes104 and 106 with freedom of movement about the ball bearing portion 107allowing the post 108 and hub 110 to rock back and forth until the domeends 116 and 120 engage the web wall 62 without encounteringinterference from the surface portions 124 a and 124 b, respectively.

[0054] In FIG. 9, a further variation of the central bearing assemblyshown in FIGS. 8A-8E is illustrated. In this version of an artificialdisc device 125, instead of having the apertured central bearing portion107 that is integrally connected to the web wall 62, upper and lowerinner bearing rings 126 and 128 are provided supported by an innerextension 130 of the web wall 62 that extends therebetween. The rings126 and 128 each have an outer arcuate bearing surface 126 a and 128 aon which the dome shells 104 and 106 ride. The rings 126 and 128 canalso translate along the web wall 62 to provide for lateral movement ofeither or both dome shells 104 and 106 during articulation of the spinesuch as when the patient bends their spine in flexion or extension. Inthis manner, the device 125 provides for an even greater range of motionthan the previously described devices as there are now three shiftinginterfaces including the innermost interface between the rings 126 and128 and web wall 62 enabling the dome shells 104 and 106 to reciprocatetherealong. At the same time, the shells 104 and 106 may be rotating inthe indents 27 and 29 and rotating about the rings surfaces 126 a and128 a, such as in the previously-described devices. For wear resistance,the rings 126 and 128 can be of a hard polyethylene material while theweb wall 62 is preferably of a more flexible or pliant material forshock absorption purposes. For sliding of the rings 126 and 128 on theweb wall 62, it can be coated with a harder material or have washers ofmetallic or a like hardness material attached to upper and lowersurfaces thereof to reduce the friction coefficient with the rings 126and 128 sliding thereon.

[0055] Referring next to FIGS. 10A-10H, an alternative artificial discimplant device 132 is illustrated in which there is an enlarged, centralbearing member 134 and an outer bearing member 136 which share thecompressive loads generated between the vertebrae 20 and 22 duringtypical spine movements. The central bearing member 134 has a post body138 that is axially elongated such that upper and lower arcuate bearingsurfaces 140 and 142 generally extend beyond corresponding upper andlower bearing surfaces 144 and 146 formed on annular body 148 of theouter bearing member 136, similar to the previously-described discimplants herein.

[0056] The outer bearing body 148 has a central through opening 150 thatis bounded by a cylindrical inner surface 152 in close confrontingrelation to outer side surface 154 on the post body 138. To provideoptimized controlled resiliency of the shape retentive bearing body 148,through apertures 156 can be formed at selected locations extendingaxially therethrough, as shown in FIG. 10D. These apertures 156 providean increase in the normal compressibility or coefficient of restitutionof the material, e.g. plastic, of the bearing body 148. Based on theposition, pattern and/or density of the through apertures 156, theflexibility or compressibility of the body 148 can be increased ordecreased in a localized fashion. Of course, these apertures 156 couldbe employed in the other disc implants and specifically the bodies ofthe outer bearings thereof in a like fashion. Similarly, thepreviously-described liquid or gel material, e.g. Hydrogel, used in theouter bearing body 17 could also be provided in the apertures 156 sothat they do not extend all the way through the body 138 and insteadserve as chambers for the visco-elastic material therein to varycompressibility of the body 148.

[0057] For instance and as shown in the plan view of FIG. 10A, thefrequency of the apertures 156 can be increased in a radially outwarddirection from the central opening 150 to the periphery of the bearingbody 148 so that in a like fashion the body 148 can be more easilycompressed toward the periphery thereof. Alternatively, the size ordiameter of the holes 156 can vary such as by having, for example,smaller size apertures 156 a closer to the central opening 150, largersize apertures 156 b closest to the radially outer periphery of the body148, with apertures 156 c having sizes intermediate those of apertures156 a and 156 b generally disposed therebetween, as shown in FIG. 10E.As is apparent, by selective spacing and/or sizing of the aperture 156,the bearing body 148 can be made to be more or less flexibly resilientat precise locations thereabout. In this manner, the bearing body 148can be stiffer in locations where load bearing is more critical and morecompressible at positions were shock absorption is more important. It isalso anticipated that the apertures 156 will provide stress relief forthe load bearing body 148 so as to increase the life thereof.

[0058] As seen in the cross-sectional views of FIGS. 10D and 10H, thepost body 138 preferably is provided with a recess in its surface 154such as annular groove 139 formed approximately midway along the bodylength between the bearing surfaces 140 and 142 thereof. By way of thisgroove 139, there is a gap 155 that is formed between the confrontingbearing surfaces 152 and 154. When the resilient body 148 of the outerbearing 136 is compressed, the gap 155 provides space into which theresilient material of the body 148 can deform and expand laterally.

[0059] An alternative disc device 175 is shown in FIGS. 11A-11D havingupper and lower disc plate members 176 and 178 with there being a loadbearing member 180 therebetween. However, unlike prior devices, thedevice 175 like other devices described herein allows for relativemovement between the vertebrae 20 and 22 and the respective vertebralengaging members 176 and 178. The plate members 176 and 178 have arcuatevertebral engaging surfaces 182 and 184 formed thereon having a gradualcurvature or slope extending from the outer periphery up toward centralaxis 186 of the device 175. As the surfaces 182 and 184 approach theaxis 186 they begin to extend more axially than radially to form centerprojections 188 and 190. These projections 188 and 190 are shown inFIGS. 11C and 11D as being provided with a tip or point end 191 and 193for piercing into the vertebral bone locating the device 175 implantedbetween the vertebrae 20 and 22 although they also could simply becurved or sloped as shown in FIGS. 11A and 11B to serve the samelocating function similar to the center arcuate surface portions ofpreviously-described devices.

[0060] Accordingly, the surfaces 182 and 184 include radially extendingbearing surface portions 182 a and 184 a that extend radially along therespective facing vertebral surfaces and central, axially extendingbearings surface portions 182 b and 184 b that serve to locate thedevice 175 while also allowing relative sliding rotation of thevertebrae 20 and 22 thereabout and specifically 3600 about device axis186 since the plate members 176 and 178 are not fixed to the respectivevertebrae 20 and 22. The center surface portion 182 b and 184 b onlyresist lateral sliding of the plates 176 and 178 by fitting incorrespondingly shaped recesses or openings in the vertebral facingsurfaces 20 and 22 a and otherwise are not fixed or fastened thereto.

[0061] As shown, the member 180 has a spherical ball configuration. Theplates 176 and 178 have arcuate recessed surfaces 192 and 194 oppositetheir surfaces 182 and 184 and in which the ball member 180 seats. Theball member 180 can be of a harder material, e.g. steel, than the softerdisc plate members 176 and 178. The materials for the members 176-180 ispreferably selected for low frictional resistance to relative slidingmovement therebetween to allow rotation of the members 176-180 such aswhen the spine is twisted and to allow relative sliding between theplate members 176 and 178 and ball 180 such as when the spine is bent inflexion and extension with the plates 176 and 178 pivoting with respectto each other. In this manner, the device 175 is bi-polar since thereare two shifting interfaces thereof, i.e. between the plates 176 and 178and the vertebrae 20 and 22 and between the ball 180 and the plates 176and 178.

[0062] FIGS. 11E-11H are views of another device 175′ similarlyconstructed to device 175 including upper and lower plates 176 and 178with a ball bearing 180 therebetween. The device 175′ also includes anannular member 196 that extends about the ball bearing 180 with theplates 176 and 178 engaged against upper and lower surfaces 196 a and196 b thereof. The annular member 196 acts as a shock absorber and canbe formed of an elastomeric or other resilient material.

[0063] As is apparent, the various forms of artificial disc devicesdisclosed herein rely on both a center bearing portion and an outer,annular bearing portion extending about the center bearing portion toprovide implants that resist migration without relying on disc fixingmechanisms such as intrusive bone fasteners, clamps and the like whilealso avoiding subsidence problems about the center bearing portion. Tothis end, the upper and lower arcuate surfaces of the center bearing orbearing portion or bearing assembly seat in correspondingly shapedrecesses 27 and 29 in the vertebral surfaces 20 a and 22 a to locate theartificial disc device between the vertebrae 20 and 22. The interfacebetween the center bearing surface portions and the recesses 27 and 29is preferably a sliding one, i.e. not fixed, to substantially providethe vertebrae with their normal range of motion relative to each otherwith the discs implanted therebetween. And because of the enlarged axialspacing of the surface portions relative to the outer bearing portion,be they formed on separate components such as the dome shells or on asingle part such as center ball or post bearings, the convex curvatureof the center surface portions seated in the concave recesses providesresistance against migration or lateral shifting of the device out frombetween the vertebrae.

[0064] Extending about these axially projecting center bearing surfaceportions are outer bearing surface portions that also extend radiallyoutwardly therefrom, generally with a more gradual curvature or with aflat configuration. As shown, the outer bearing surface portions extendso that their radial outer ends are close to the periphery of therespective vertebral bodies thereabove and therebelow. Accordingly, theupper outer bearing surface portion is generally lower than the axiallyprojecting upper center bearing surface portion, and they form ajuncture at which the direction in which the surface portions of thedisc device for engaging the vertebrae changes or transitions from oneextending more axially to one extending more radially. This juncture isa direction transition area and does not necessarily mean that thesurface portions are joined thereat, such as can be seen with thepreviously-described ball bearing 12 and ring bearing 14 which areseparate components with the ring bearing 14 extending annularly aroundthe ball bearing 12 so as to allow for relative movement therebetween.Similarly, the lower outer bearing surface portion is generally higherthan the axially projecting lower center bearing surface portion, and attheir juncture the direction of the vertebral engagement surface portionof the device also changes as described above with respect to the uppervertebral engagement surface portions. In this manner, these radiallyextending outer surface portions limit the ability of the vertebrae ortheir attached end plates to subside around the center bearing. If thereis any subsidence, its extent is limited by the axial spacing of theupper and lower outer bearing surface portions. In other words, in thearea taken up by the artificial disc, the spacing of the upper and lowervertebrae can not be less than the spacing between the outer bearingsurface portions, thereby limiting subsidence problems accordingly.

[0065] In another version of a disc device 200 in accordance with theabove principles, upper and lower arcuate center bearing surfaceportions 202 and 204 that are convexly curved are provided for locatingthe device 200 between adjacent vertebrae in corresponding arcuateconcave recesses formed therein. Upper and lower outer bearing surfaceportions 206 and 208 extend annularly about respective center bearingsurface portions 202 and 204 and limit subsidence between the vertebraeabout the center bearing portion 210 of the device 200. The uppersurface portions 202 and 206 are formed integrally on an upper platemember 212, and the lower surface portions 204 and 208 are formedintegrally on a lower plate member 214. The plate members 212 and 214can be of a hard biocompatible material such as titanium coated with apyroletic carbon. Like previously-described discs, the center bearingsurface portions 202 and 204 are spaced by an axially greater distancethan the outer bearing surface portions 206 and 208, and they have asmaller radius of curvature than the more gradual curvature of thesurface portions 206 and 208. As such, as the vertebral engaging surfaceportions extend away from the disc axis 216, there is upper and lowerjunctures 218 and 220 where the direction and configuration of thesurface portions undergo an abrupt change from one where the surfaceportion 202 or 204 extends more axially versus one where the surfaceportion 206 or 208 extends more radially to provide subsidenceresistance about the center bearing 210. To this end, the plate members212 and 214 include respective small, axial projections 213 and 215 thatare centrally disposed relative to disc axis 216 and on which therespective center bearing surface portions 202 and 204 are formed.

[0066] As part of annular, outer bearing portion or assembly 222extending about the center bearing assembly 210, an annular load bearingportion or member 224 is provided axially between the upper and lowerbearing plates 212 and 214. The member 224 is preferably of a resilientmaterial such as an elastomeric or resiliently compressible polymericmaterial, e.g. polyurethane and silicone combination, or a hydrogelmaterial, for taking loads that are generated between the vertebraeduring normal spinal movements. The annular member 224 has an axialthickness sized to maintain the plates 212 and 214 spaced axially by ananatomically correct distance from each other for engaging the vertebraeand keeping them properly spaced. At the same time, the resilientmaterial of the load bearing member 224 allows the plates 212 and 214 toshift or deflect relative to each other during dynamic relativemovements of the spine vertebrae 20 and 22 such as when the spine isbeing twisted and bent as in flexion or extension movements. Forexample, at one end of the disc 200, the plates 212 and 214 may bepivoting toward each other compressing the member 224 therebetween whileat a generally diametrically opposite end the plates 212 and 214 willpivot or shift away from each other allowing for expansion of theresilient material of the member 224 in this area between the plates 212and 214.

[0067] The annular bearing member 224 can be a composite to include aharder low friction wear coating on its upper and lower surfaces toallow the facing lower and upper surfaces of the respective upper andlower bearing plates 212 and 214 to minimize wear in this interface areasuch as when compressional and/or torsional forces are appliedtherebetween. Alternatively, upper and lower annular washers or wearplates 226 and 228 can be inserted in the interfaces between the upperbearing plate 212 and the load bearing member 224 and the lower bearingplate 214 and the load bearing member 224 to allow the plates 212 and214 to have a low friction surface in engagement therewith.

[0068] The annular configuration of the load bearing member 224 of theouter bearing portion 222 forms an interior central space 230 in which abumper or plug member 232 is provided as part of the center bearingportion 210 of the device 200. The bumper member 232 fits somewhatloosely in the interior space 230 and is of a harder material having ahigher modulus of elasticity than the outer bearing member 224. Thus,the plug member 232 is operable during high impact loading on thevertebrae to keep the annular member 224 from deforming too much andoverloading. In normal loading conditions, there is a spacing betweenthe upper plate member 212 and the bumper member 232. The harder plugmember 232 allows the annular member 224 to be softer so that itscushioning function between the vertebrae can be maximized. At the sametime the material of the member 224 needs to be of sufficient stiffnessor resiliency so as to be substantially shape retentive for maintainingstability between the vertebrae over millions of cycles and withoutexperiencing undesirable material creep or plastic deformation due tothe heavy loading it will undergo.

[0069] As can be seen in FIGS. 12A and 12C, the plates 212 and 214 haverespective arcuate projections 234 and 236 that extend toward each otherin the interior space 230. The plug member 232 has upper and lowerarcuate recesses 238 and 240 concavely configured to mate with theconvex configuration of the arcuate projections 234 and 236,respectively. The relative sizing of the space 230 and the plug member232 therein is such that when the plug member 232 rests on the lowerplate 214 via seating of the projection 236 in the recess 240, therewill be an axial gap 242 between the plug 232 and the upper plate 212and specifically the respective surface 238 and projection 234 thereof.Accordingly, the annular member 224 has a greater axial thickness thanthe plug member 232. The space 230 has a larger diameter than the plugmember 232 so that there is a generally lateral space between the innersurface 224 a of the annular member 224 and the plug member 232 allowingfor lateral deformation of the resilient member 224 when loaded. Whenthe vertebrae are overloaded such as due to shock or high impact loads,the normal loading ring member 224 is compressed taking up the axial gap242 such that the projection 234 engages the harder plug member 232 inthe recess 238 thereof. In this manner, further compression andoverloading of the resilient member 224 is avoided. Also, engagement ofthe projections 234 and 236 in their recesses 238 and 240 resistsrelative lateral shifting between the plates 212 and 214, and theannular member 222.

[0070] It is also contemplated that the annular member 224 and plugmember 232 could be integrally formed with one another, although havingthe members 224 and 232 as separate components is the preferred form forthe present disc device 200.

[0071] As best seen in FIG. 12C, the arcuate projections 234 and 236 arelarger than the respective arcuate surface portions 202 and 204. Theprojections 234 and 236 are centrally disposed relative to axis 216 andextend radially for a greater distance on either side of axis 216 thando the arcuate surface portions 202 and 204 so that there is a greaterbearing surface interface between the plate projections 234 and 236 andthe plug member 232 than between the locating surface portions 202 and204 and the vertebrae. As such, when the plug member 232 is loaded, itprovides relatively large bearing surfaces for the plates 212 and 214,and also allows for pivoting between the plates 212 and 214 with theplate central projections 234 and 236 sliding in respective recesses 238and 240 and with compression and expansion of generally diametricallyopposed portions of the member 224 depending on the exact location ofthe loads placed on the device 200. Alternatively, the surface portions202 and 204 can be similarly sized to the projections 234 and 236 oreven larger for maximizing the bearing surface area they provide betweenthe device and the vertebrae.

[0072] In FIGS. 12D and 12E, the disc device 200 is shown withmodifications including an annular sheath 244 that extends about theouter periphery of the device 200. The sheath 244 includes upper andlower lips 246 and 248 and that grip around and onto the upper and lowersurfaces 206 and 208, respectively, of the outer bearing assembly 222 tohold the device 200 in its assembled form for implantation.Alternatively, a bag completely encasing the device 200 could beemployed. Also, a retaining structure, generally designated 250, can beprovided between the plates 212 and 214 and the annular member 224 forresisting relative lateral shifting between the plates 212 and 214, andthe member 222, as well as resisting relative rotational shiftingtherebetween for keeping these disc components aligned. Projecting posts252 and 254 can project down from the underside of the upper plate 212,and posts 256 and 258 can project up from the upper side of the lowerplate 214. Corresponding aperture pairs 260 and 262 can be formed in theupper and lower surfaces of the annular bearing member 224 for receivingthe respective post pairs 252, 254 and 256, 258 therein, as can be seenin FIG. 12E. Alternatively, the location of the posts and aperturescould be reversed. In another alternative form of retaining structure250, upper and lower annular grooves 261 (upper groove 261 shown inghost in FIG. 12D) can be formed in upper and lower surfaces of theannular bearing member 224 for receipt of corresponding upper and lowerraised ridges formed on the resilient annular member 224. Since the planshape or configuration of the plates 212 and 214 and member 224 areother than circular, it is desirable for the ridges and grooves to besimilarly configured so that relative rotational sliding as well astranslational or lateral sliding between these components is resisted.Again, the components on which the cooperating grooves and ridges areformed can be reversed from that described above.

[0073] Instead of the posts/recess or groove/ridge structure 250, thestructure 250 can be provided at the periphery of the device 200, asshown in FIG. 12F. The upper plate 212 includes a downwardly extendingperipheral lip projection 263, and the lower plate 214 includes anupwardly extending peripheral lip projection 264. The resilient member224 is provided with peripheral grooves 266 and 268 in which the lips262 and 264 extend so as to restrain the member 224 against lateral androtational shifting relative to the plates 212 and 214.

[0074] FIGS. 12G-12I show device 200 modified to include upper and lowerrecessed channels 270 formed in the upper and lower surfaces of theannular member 224 that extend from the inner, axially extending surface224 a to the outer peripheral surface 224 b of the member 224 to formopenings at each surface. In this way, the interior space 230 in whichthe plug member 232 is received communicates with the space external tothe device 200 via the flowpaths provided by the channels 270. Thus, thechannels 270 allow for fluid flow into and out from the device betweenthe plates 212 and 214 and the annular member 224. The channels 270 alsokeep vacuum conditions from developing in the space 230 as its volumecontinually varies with vertebral movements and thus the channels 270serve as a vacuum breaker for the device 200. The channels 270 can beprovided in a radial pattern so that there are several pairs of channels270 extending in radially opposite directions from the center space 230,as best seen in FIG. 12H.

[0075] While there have been illustrated and described particularembodiments of the present invention, it will be appreciated thatnumerous changes and modifications will occur to those skilled in theart, and it is intended in the appended claims to cover all thosechanges and modifications which fall within the true spirit and scope ofthe present invention.

We claim:
 1. A spinal artificial disc device for being implanted betweenadjacent axially spaced upper and lower vertebrae, the artificial discdevice comprising: upper and lower central bearing surface portionshaving an arcuate, generally axially extending configuration forprojecting toward and slidingly engaging against respective facingvertebral surfaces; upper and lower outer bearing surface portions thatgenerally extend radially outward from corresponding upper and lowercentral bearing surface portions for projecting along the vertebralsurfaces, the central bearing surface portions being axially spaced by agreater distance than the radially outer bearing surface portions withthe central and outer bearing surface portions sharing compressive loadsgenerated during spinal movements for minimizing vertebral subsidenceabout the axially enlarged central bearing surface portions; andjunctures between the upper and lower central bearing surface portionsand the corresponding upper and lower outer bearing surface portions atwhich the bearing surface portions change directions from extendinggenerally axially on the central bearing surface portions to extendinggenerally radially on the outer bearing surface portions.
 2. Theartificial disc device of claim 1 including: a central ball bearinghaving an outer spherical surface that includes the central arcuatebearing surface portions; and an outer annular bearing having the outerbearing surface portions formed thereon and including an inner sidesurface facing the central bearing spherical surface and beingconfigured to allow relative rotation between the central sphericalbearing and the annular bearing.
 3. The artificial disc device of claim2 wherein the inner side surface has a flat configuration extendinggenerally axially and radially spaced from the spherical surface or anarcuate configuration having a radius of curvature similar to that ofthe spherical surface.
 4. The artificial disc device of claim 1 whereinthe upper central and outer bearing surface portions are formed on anupper plate member and the lower central and outer bearing surfaceportions are formed on a lower plate member.
 5. The artificial discdevice of claim 4 including an annular member between the upper andlower plate members of a predetermined resilient material for providinga cushioned support therebetween, and a plug member about which theannular member extends having an axial thickness less than that of theannular member and being of a predetermined material that is harder thanthe resilient material of the annular member to limit overloadingthereof.
 6. The artificial disc device of claim 1 including: a bearingbody having a central enlarged arcuate bearing portion, and an outerbearing portion on which the outer bearing surface portions are formed;and upper and lower dome shells configured to slide on the arcuatebearing portion and having the respective upper and lower centralbearing surface portions thereon.
 7. The artificial disc device of claim6 wherein the enlarged arcuate bearing portion has a sphericalconfiguration.
 8. The artificial disc device of claim 1 wherein thecentral arcuate surface portions have a greater curvature than the outerbearing surface portions.
 9. The artificial disc device of claim 8wherein the outer bearing surface portions are curved, flat, orcontoured.
 10. The artificial disc device of claim 1 wherein the upperand lower outer bearing surface portions are formed on an outer bearingportion which has radially inner surfaces adjacent the central bearingsurface portions configured to allow relative movement therebetween. 11.The artificial disc device of claim 10 wherein the outer bearing portionincludes a body having an annular portion, and a central bearing portionwith the outer bearing annular body portion extending about the centralbearing portion and central bearing surface portions.
 12. The artificialdisc device of claim 11 wherein the annular outer bearing portion andcentral bearing portions are distinct members.
 13. The artificial discdevice of claim 11 wherein the central bearing portion includes acentral body portion integral with outer bearing annular body portion.14. The artificial disc device of claim 13 wherein the central andannular body portions include a radially extending web wall that spacessaid body portions by a predetermined gap spacing; and upper and lowershells of the central bearing portion which have the respective upperand lower arcuate central surface portions thereon with the shells andcentral body portion being configured to permit sliding of the shells onthe central body portion.
 15. The artificial disc device of claim 1including an outer bearing portion extending about the central bearingsurface portions and having a body with the outer bearing surfaceportions formed thereon, the body of the outer bearing portion being ofa resilient material and the central bearing surface portions being of amaterial harder than the resilient material, and a compression limiterin the body of the outer bearing portion that is of a material harderthan that of the outer bearing portion body to resist deformationthereof under compressive loads.
 16. The artificial disc device of claim15 wherein the outer bearing portion includes an annular body portion,and the compression limiter comprises a ring embedded in the annularbody portion.
 17. The artificial disc device of claim 1 wherein theouter bearing surface portions each have a perimeter that generallydefines one of a heart shape and an oval shape.
 18. The artificial discdevice of claim 1 including an outer bearing portion extending about thecentral bearing surface portions and having the outer bearing surfaceportions formed thereon, and a cushioning material disposed axiallyintermediate the outer bearing surface portions.
 19. The artificial discdevice of claim 18 wherein the outer bearing portion comprises upper andlower annular plates having the respective upper and lower centralbearing surface portions formed thereon, and the cushioning materialextends between the plates to bias the plates apart and allow resilientshifting of the plates relative to each other during vertebralmovements.
 20. The artificial disc device of claim 1 including anarcuate central bearing portion and upper and lower shells on which therespective upper and lower central bearing surface portions are formedand which are slidingly supported on the central bearing portion. 21.The artificial disc device of claim 20 wherein the central bearingportion has an axial opening, and at least one of the shells includes aprojection extending in the opening to limit axial shifting of theshells toward each other.
 22. The artificial disc device of claim 20wherein the arcuate central bearing portion includes a radiallyextending wall and upper and lower arcuate bearing rings supported forlateral sliding on the wall disposed therebetween with the shellssupported for sliding over the bearing rings to allow for lateralmovement of the shells during vertebral movements.
 23. The artificialdisc device of claim 1 including an outer bearing portion on which theouter bearing surface portions are formed and having a body of amaterial having a predetermined compressibility and a plurality ofapertures in the body to vary the compressibility thereof from thepredetermined compressibility.
 24. The artificial disc device of claim23 wherein the body has a predetermined number, arrangement and sizingof the apertures to provide for a controlled variation of thecompressibility of the body.
 25. The artificial disc device of claim 1wherein the central bearing surface portions are formed on a centralbearing and the outer bearing surface portions are formed on an outerbearing including an annular body that extends about the centralbearing, the central bearing having a body that is axially enlargedrelative to the annular body.
 26. The artificial disc device of claim 25wherein the central bearing body comprises a generally spherical ballbody or an axially elongated post body.
 27. The artificial disc deviceof claim 1 including a bearing body having an axially enlarged centralbearing body portion and an outer annular body portion extending aboutthe central body portion, and a web wall integrally interconnecting thecentral and outer body portions, and upper and lower shells configuredto slide on the central bearing body portion and having the respectiveupper and lower central bearing surface portions formed thereon.
 28. Anartificial disc device for being implanted between upper and lowervertebrae, the artificial disc device comprising: a central bearing forbeing inserted between the upper and lower vertebrae; upper and lowerarcuate central bearing surface portions of the central bearing thatseat in arcuate recesses formed in the respective facing vertebralsurfaces to resist migration of the central bearing from between thevertebrae; an annular outer bearing extending around the central bearingso that the outer bearing is kept between the upper and lower vertebraeby the central bearing; and upper and lower outer bearing surfaceportions of the outer bearing extending radially outward from thecorresponding upper and lower bearing surface portions of the centralbearing for sharing loads therewith to minimize highly localized loadingon the bearing surface portions.
 29. The artificial disc device of claim28 wherein the outer annular bearing has an inner diameter, and thecentral bearing is sized to be in clearance with the annular bearinginner diameter to allow relative movement therebetween.
 30. Theartificial disc device of claim 28 wherein the central bearing has agenerally spherical outer surface including the central bearing surfaceportions, and the outer bearing includes a central axial through openingin which the central bearing resides and an arcuate inner side surfaceextending about the opening and facing the spherical central bearing,the arcuate side surface generally having the same radius of curvatureas that of the spherical outer surface to allow substantially freerotation of the central bearing seated in the vertebral recesses. 31.The artificial disc device of claim 30 wherein the spherical outersurface has a predetermined diameter, and the outer bearing upper andlower surface portions are axially spaced by a distance that is lessthan the predetermined diameter so that the central spherical bearing isaxially enlarged relative to the annular outer bearing.
 32. Theartificial disc device of claim 28 wherein the upper and lower surfaceportions of the central bearing engaged in the vertebral recesses areaxially spaced by a greater distance than the upper and lower surfaceportions of the outer bearing which have an axial spacing sized tomaintain a generally anatomically correct spacing between the upper andlower vertebrae engaged therewith.
 33. The artificial disc device ofclaim 28 wherein the upper and lower surface portions of the outerbearing have an arcuate configuration with a more gradual curvature thanthe arcuate surface portions of the central bearing for generallyconforming to the shape of the facing vertebral surfaces.
 34. Theartificial disc device of claim 28 wherein the annular outer bearing hasa generally wedged configuration including an axially enlarged sectionbetween the upper and lower surface portions for optimizing fit of theouter bearing between the vertebrae.
 35. The artificial disc device ofclaim 28 wherein the outer annular bearing extends about a disc axis andcomprises upper and lower annular plates with the upper bearing surfaceportion on the upper plate and the lower bearing surface portion on thelower plate, the plates being axially spaced and extending generallytransverse to the disc axis.
 36. The artificial disc device of claim 35wherein the plates have a cushioning material in the axial spacetherebetween to provide for resilient shifting of the plates relative toeach other and biasing the unloaded plates to a generally parallelorientation thereof.
 37. The artificial disc device of claim 36 whereinthe central bearing has a generally spherical outer surface includingthe arcuate surface bearing portions, and the annular plates eachinclude a central opening having a maximum diameter that is less thanthat of the spherical outer surface for providing the axial spacing ofthe plates in close fit with the central bearing outer surface.
 38. Theartificial disc device of claim 28 wherein the outer annular bearing hasa central axial through opening, and the central bearing has a body thatis axially elongated to extend through the central opening with theupper and lower arcuate surface bearing portions extending axiallybeyond the corresponding upper and lower outer bearing surface portions.39. The artificial disc device of claim 38 wherein the outer annularbearing is of resilient material and has an inner surface bounding thethrough opening, and the axially elongated body includes an outer sidesurface that is in close confronting relation to the annular bearinginner surface and which has an annular groove to provide a gap betweenthe confronting bearing surfaces into which the resilient material ofthe outer annular bearing can deform when loaded.
 40. The artificialdisc device of claim 28 wherein the central bearing is of a hardermaterial than the outer bearing to maintain conformity of the arcuatesurface portions in the vertebral recesses.
 41. The artificial discdevice of claim 28 wherein the outer bearing is of resilient material toallow the outer bearing to resiliently deform under compressive loadingforces.
 42. The artificial disc device of claim 28 wherein the outerbearing has an outer wear layer including the bearing surface portionsthereof, and an inner cushion portion with the outer wear layer being ofharder material than the inner core cushion portion.
 43. An artificialdisc device for being implanted between axially spaced upper and lowervertebrae, the artificial disc device comprising: upper and lower platemembers for engaging facing surfaces of the respective upper and lowervertebrae; a central projection on each of the plate members extendingaxially and having an arcuate surface thereon for sliding in an arcuaterecess in the vertebrae with which the arcuate surface is slidinglyengaged; an annular load bearing member between the plate members foraxially spacing the plate members and being of resilient material toallow shifting of the plate members toward and away from each other withresilient deformation of the annular member; and a bumper member aboutwhich the annular member extends and being of a harder material than theannular member to limit deformation of the annular member.
 44. Theartificial disc device of claim 43 wherein the annular load bearingmember is axially thicker than the bumper member so that there is spacebetween the upper plate member and the bumper member during normalloading conditions of the spine.
 45. The artificial disc device of claim43 including low friction bearing surfaces between the annular memberand the plate members to minimize wear therebetween.
 46. The artificialdisc device of claim 43 wherein the upper plate and lower plate includearcuate central projections extending toward each other, and the bumpermember has upper and lower arcuate recesses configured for mating andsliding engagement with the corresponding upper plate and lower plateprojections.
 47. The artificial disc device of claim 43 including asheath or bag for holding the plate members, annular load bearing memberand bumper member together in assembled form during implantation. 48.The artificial disc device of claim 43 wherein the plate members andannular member include retaining structure therebetween that resistslateral and rotational shifting of the plate members relative to theannular member.
 49. The artificial disc device of claim 48 wherein theretaining structure comprises annular grooves in one of the annularmember and the plate members and projections in the other of the annularmember and the plate members that extend into the grooves.
 50. Theartificial disc device of claim 43 wherein the annular member defines acentral interior space in which the bumper member is loosely disposedand includes openings to the interior space and to exterior of theannular member to provide a flowpath therebetween.
 51. The artificialdevice of claim 43 wherein the annular member and at least one of theplate members include a channel therebetween for providing fluid flowbetween the interior and exterior of the disc device.
 52. The artificialdisc device of claim 51 wherein the annular member has upper and lowersurfaces facing the respective upper and lower plate members, and thechannel includes a plurality of radially extending channels formed inthe upper and lower surfaces of the resilient annular member.
 53. Theartificial disc device of claim 43 wherein the resilient material of theannular load bearing member comprises hydrogel.
 54. An artificial discdevice for being implanted between upper and lower vertebrae, theartificial disc device comprising: upper and lower arcuate bearingshells for slidingly engaging against respective facing surfaces of theupper and lower vertebrae; a central bearing portion having an arcuateouter surface that supports the shells for sliding thereon to allow fordifferential shifting between the relative movement of the shells andthe engaged vertebrae and of the shells and the central bearing portionduring vertebral movements; and an annular outer bearing portionextending around the central bearing portion for load sharing with thebearing shells.
 55. The artificial disc device of claim 54 wherein thecentral bearing portion has a generally spherical configuration and theshells have a dome configuration for sliding on the spherical centralbearing portion.
 56. The artificial disc device of claim 55 wherein thespherical central bearing portion has a predetermined diameter, and thedome shells have a maximum diameter that is less than the predetermineddiameter.
 57. The artificial disc device of claim 54 including a webwall that interconnects and spaces the central and outer bearingportions laterally from each other to keep interference between thesliding bearing shells and the outer bearing portion to a minimum. 58.The artificial disc device of claim 57 wherein the web wall is integralwith the central and outer bearing portions.
 59. The artificial discdevice of claim 54 wherein the central bearing portion and annular outerbearing portion are laterally spaced from each other to form a gaptherebetween in which the shells can slide and the annular bearingportion has an inner side surface that extends axially to maximizesizing of the recesses.
 60. The artificial disc device of claim 54wherein annular outer bearing portion is of resilient material and hasan outer peripheral surface including upper and lower flanges and aconcave groove between the flanges to optimize flexibility of theflanges under compressive loading.
 61. The artificial disc device ofclaim 54 wherein the outer bearing portion includes a core of cushioningmaterial for shock absorbtion and upper and lower bearing surfaces ofhard material for wear resistance.
 62. The artificial disc device ofclaim 54 wherein the central bearing portion includes an axial throughopening, and the shells include projections that extend in the throughopening and cooperate to limit compression of the central bearingportion and shifting of the shells axially toward each other.
 63. Theartificial disc device of claim 54 including a web wall interconnectingthe bearing portions extending laterally therebetween, and the outerbearing portion includes an inner extension of the web wall and upperand lower arcuate bearing rings that support the respective upper andlower shells for sliding thereon and which are supported for lateralsliding on the web wall including the extension thereof.